Thursday 3 October 2013 10.24 EDT
First published on Thursday 3 October 2013 10.24 EDT

Silk Road, the best-known underground marketplace for the trade of illegal drugs on the internet, has been shut down leaving a large hole in the internet's underworld.

Described by FBI special agent Christopher Tarbell as "the most sophisticated and extensive criminal marketplace on the internet today", Silk Road acted like an eBay for the trade of illegal substances.

It operated as a "hidden" site, which was only accessible to people using the sophisticated anonymous browsing service known as Tor.

Operated by a network of volunteers, Tor provides encryption and identity protection, allowing users to avoid surveillance and traffic interception as well as circumvent internet censorship.

Tor is a favourite of whistleblowers and political activists, including Edward Snowden, due to its privacy protection, while its user base has topped an estimated 1.2 million users.

Tor also allows sites to exist only within its secure network, often referred to as the "dark web", not on the open internet, which is what allowed Silk Road to stay hidden and protected for so long, despite efforts from security services and politicians, including US senator Chuck Schumer, who vowed in 2011 to have it shut down.

Silk Road will almost certainly be replaced

Although it was certainly the most high profile, Silk Road was not the first illegal marketplace hidden within the dark web or on the open internet.

"Silk Road will almost certainly be replaced by a copycat-like site, as has been the case in carder markets where people trade fraudulent credit card information. Those kinds of places have been shut down in the past and very, very quickly replaced by others," said Rik Ferguson, vice-president of security research at Trend Micro, talking to the Guardian.

Sites similar to Silk Road already exist within the Tor network. Two stores called Atlantis and Sheep Marketplace offer illegal drugs, equipment and services akin to Silk Road.

However, some sites go further – Bitcoin-powered shop called Black Market Road, for instance, also sells illegal weapons, something Silk Road withdrew after high profile shootings in the US.

"The are a multitude of online marketplaces for the trade of illegal goods, not all hidden within what we would call the dark web, but on the regular open internet.

"Forum-based shop fronts exist, where it's not just one individual in charge of buying and selling, but it's a co-operative that's based on trust. They predated Silk Road by a very long way, and continue to thrive to this day," said Ferguson.

"It's a very established underground economy – where there is a void, there's a niche."

No real compromise of Tor

Due to the fact that Silk Road existed purely within the Tor network, there was a possibility that the anonymity and security of the service and software could have been compromised, although that seems to not be the case.

"Nothing about this case makes us think that there are new ways to compromise Tor (the software or the network). The FBI says that their suspect made mistakes in operational security, and was found through actual detective work," said the Tor project in a blog post.

Ferguson agreed: "[Alleged Silk Road owner and operator Ross William] Ulbricht was tracked via good traditional investigative techniques, research and intelligence, tracking his mistakes on the open internet, such as making postings on forums in his own name, while tracing illegal packages that were received at the US border.

"I don't think there will be a huge impact on people's perception of the anonymity of Tor as there was no real compromise of the integrity or security of Tor."